java.lang.ClassCastException: java.util.HashMap cannot be cast to custom data class

Question

I upload my data class object to Firestore, it uploads fine, when I try to download it from another activity the java.lang.ClassCastException occurs. I need the object of Cart class in AddToCart.java to be saved in the Firestore (Success) and get it back in Cart.java (Failure). PLEASE HELP!!!!!

Here is the how I am putting data into the Firestore:

 private void updateFirestore() {

    Map cartList = new HashMap<String,CartModel>();

    //I put data into the map

    FirebaseFirestore firestoreRef = FirebaseFirestore.getInstance();
    firestoreRef.collection(colloctionKeyTitle)
                  .document(currentSelectedModel.getUserId()).set(cartList)

Here, the map with one key value is uploaded to firestore:

NOW, here is the code to get this map back.

 FirebaseFirestore firestoreRef = FirebaseFirestore.getInstance();

    Task<DocumentSnapshot> documentSnapshot = firestoreRef.collection(COLLECTION_ID).document(userId).get()
            .addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                @Override
                public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                    cartList = task.getResult().getData();
                    if (cartList != null) {
                        if (!cartList.isEmpty()) {
                            for (String key : cartList.keySet()) {
                                Object object = cartList.get(key);// In object variable I see my data when debug, but app crashes on next line.
                                Constant.listCartItems.add((CartModel) object); //this is the line where error occur.
                            }
                        }

                    }
                }
            });

Here is my CartModel.java (Data class)

public class CartModel {
private String productTitle,productPrice, featuredImagePath, quantity;

public CartModel(String productTitle, String productPrice, String featuredImagePath,String quantity) {
    this.productTitle = productTitle;
    this.productPrice = productPrice;
    this.quantity=quantity;
    this.featuredImagePath = featuredImagePath;
}

public CartModel(String productTitle, String productPrice, String featuredImagePath) {
    this.productTitle = productTitle;
    this.productPrice = productPrice;
    this.featuredImagePath = featuredImagePath;
}

public CartModel() {

}


public String getQuantity() {
    return quantity;
}

public void setQuantity(String quantity) {
    this.quantity = quantity;
}

public String getProductTitle() {
    return productTitle;
}

public void setProductTitle(String productTitle) {
    this.productTitle = productTitle;
}

public String getProductPrice() {
    return productPrice;
}

public void setProductPrice(String productPrice) {
    this.productPrice = productPrice;
}

public String getFeaturedImagePath() {
    return featuredImagePath;
}

public void setFeaturedImagePath(String featuredImagePath) {
    this.featuredImagePath = featuredImagePath;
}

}

Answer 1

I see now in your database structure, that you hold more than one object of type CartModel inside that document. To solve this, get the data as a Map like in the following line of code:

Map<String, Object> map = document.getData();

Iterate through the map and get all CartModel objects from it. That's it.

Answer 2

I think issue in the Constant object. There is a mismatch between Constant.listCartItems and the object you put into the map.

Answer 3

You have two ways to solve your issue :

Solution one

cast your Object to the correct one :

Object object = (MyObject) cartList.get(key);
                 ^^^^^^^^

Solution two

You have to set the Key and Value type :

Map<Key, Value> cartList = new HashMap<String,CartModel>(); 
    ^^^   ^^^^